Application for R21, NOT-AI-02-023, Biodefense and Emerging Infectious Diseases Research Anthrax toxin, isolated from the bacterium, Bacillus anthracis, enters human cells and disrupts cellular function. The toxin consists of a receptor binding component, protective antigen (PA) which can associate with the enzymatic components, edema factor (EF) and/or lethal factor (LF) to form the anthrax toxin. The toxin binds a cell surface receptor which mediates the internalization of the toxin complex. Recently, work from the laboratories of John Young and John Collier identified the receptor for the anthrax toxin, named the anthrax toxin receptor (ATR; Bradley et al., 2001). Since the ability of the anthrax toxin to cause harm is dependent upon receptor binding, targeting the anthrax receptor might provide additional therapies that could be useful even after suspected exposure to anthrax spores. In many cases, signaling downstream of cell surface receptors involves the activation of protein and lipid kinases. Successful use of the small molecule kinase inhibitor Gleevec in chronic myelogenous leukemia has shown that targeting kinases might provide an efficient means to treat various diseases. This goal of this project is to study the ATR signaling pathway in order to identify key effector molecules as targets for inhibition. The role of ATR in mediating toxin internalization will be dissected using biochemical and immunofluorescence methods in mammalian cells. The zebrafish will be used as an animal model to study ATR function in vivo and to assess its potential as an animal model for testing drugs aimed at blocking toxin action. The applicant has 3 specific aims which will be undertaken in collaboration with the Young and Collier labs. Aim 1. To investigate the role of the cytoplasmic domain of the anthrax receptor for potential therapeutic intervention. Aim 2. To determine the physiological role of the anthrax receptor by functional interference during normal embryonic development in the zebrafish. Aim 3. To examine anthrax toxicity in the zebrafish for use as an additional inexpensive model system for drug or vaccine testing.